JEC COMPOSITES MAGAZINE - Issue #78 - January/February 2013 - 52

laminate

stress from curing.
Gaps and laps are
not expected to
affect the properties along the one
axis. All layers
are mechanically
and thermally
compatible. There
is no tendency for
wrinkle to form.
Products made
from one-axis
layup are therefore
more defect-tolerant.

Fig. 3: A 3 steps production

approach, where ply combinations are
limited in discrete numbers, and not
continuous. The hundreds or thousands
of potential stacking permutations and
sequences are therefore not optimized in
practice.

One-axis layup
Another important advantage of C-PlyTM
is its one-axis layup. Instead of 3- or
4-axis layup in the black aluminium design, C-Ply with one or two off-axis plies
plus [0] can lay up a structure in stacking
fabric or tape along a single axis. The
time savings are in hundreds of percent,
depending on the length-to-width of the
composite component. The productivity
of each automated tape laying (ATL)
machine can be increased significantly.
For very long components such as spars
and stringers, the speed can be increased
by an order of magnitude.
Being homogenized, optimum tapering
can be defined by topology optimization
tools. Ply drop can be more easily done
because in-plane symmetry need not
be maintained. Plies or bi-angle layers
can be dropped at any location along
the thickness of the laminate. Since it
is a one-axis layup, ply or layer drop is
transverse to the single axis. With ATL,
there is a phenomenal decrease in the
layup time, as well as quality of the
product. With one-axis layup, there is no
transverse layer likely to cause residual

Thin plies
C-PlyTM is made of 2 or 3 thin plies.
The ply thickness is half or less that of
conventional plies, at 75 gsm compared with normal 150 gsm conventional
unitape. Thin plies contribute to several
critical features of C-PlyTM. They result in
stronger and tougher laminates because
the number of plies for a given laminate thickness is doubled or more; i.e.,
a laminate with 50 conventional plies
will have 100 or more thin plies. With a
finer structure, each ply accounts for a
smaller percentage of the total laminate.
At the same time, thinner plies help
eliminate microcracks. A part can be
loaded and unloaded without damaging
the laminate. A finer structure is more
likely to reach a higher strength and
resistance to delamination. In C-PlyTM,
each ply is made thinner by a spreading
process, resulting in a higher quality ply.
The resulting laminate can be designed
for higher strength and resistance to
delamination.

Conclusions
C-PlyTM offers many design and manufacturing advantages over conventional
unitape. First, the traditional design rules
of black aluminium are no longer necessary and, in fact, should be superseded by
more effective ones. Laminates should be
produced by stacking multiple identical
sub-laminates. A typical C-PlyTM sublaminate is [0/25], with a total weight of

52 jec composites magazine / No78 January - February 2013

150 gsm and a 0.125 mm thickness. In
practice, each sub-laminate should be a
small fraction of the total laminate. We
recommend the fraction to be 1/16; i.e.,
if a laminate is 1.6 mm, each sub-laminate should be 0.1 mm or less.
Such a laminate is homogenized and
the stretching and bending stiffness
becomes the same. The laminate would
be essentially symmetric, and quasiisotropic, orthotropic or anisotropic
(not balanced). From a basic bi-angle
C-PlyTM, it is possible to produce 3- and
4-angle laminated structures.
For automated tape laying machines,
many structures can be made with a
one-axis layup for panels with C-PlyTM.
All components can be optimized in
terms of geometry and loading to take
full advantage of this shallow-angle,
thin-ply concept. A 50% weight saving
is achievable. Being made of thin plies,
these panels can often offer design
options for minimum gage not possible
with thick unitape. Equally important are
the increased productivity (due to faster
layup times) and improved quality that
result from having fewer layup axes than
in traditional 3- or 4-axis design.
The current generation of C-PlyTM can
be extended to unlimited combinations
of material, geometric and processing
options. For example, carbon/glass
hybrids, thick-thin ply combinations, different layup axes and different tapering
are possible for the two plies.
Stanford University and Chomarat are
developing the concept with key aerospace OEMs, one of whom considers
C-Ply TM as a key material for what they
call “second-generation composites”. The
partners wish to collaborate with companies interested in higher performance
C-PlyTM fabric and prepreg in order to
demonstrate the feasibility of simultaneous weight and cost reductions. n
More information:
www.chomarat.com
http://www.chomarat.com
JEC COMPOSITES MAGAZINE - Issue #78 - January/February 2013

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